This summary distills the most critical elements of the New World Screwworm Response Playbook, released by USDA APHIS in October 2025, into action items for cattle ranchers in the event of New World Screwworm (NWS) detection the in United States. The playbook highlights immediate response priorities, protective actions, and key biosecurity measures to reduce risk and maintain continuity of business during an outbreak. NWS poses a major threat to livestock health, ranch profitability, and the U.S. cattle industry. Rapid detection and coordinated control with federal and state animal health officials is essential to prevent NWS spread and re-establishment.

Understanding the Threat

The NWS is a parasitic fly whose larvae infest open wounds in the living flesh of all warm-blooded animals, including livestock, wildlife, and humans. NWS myiasis, or infestation, occurs when female flies lay eggs at the edges of wounds or on mucous membranes like nostrils, ears, eye orbits, the mouth, or genitalia. Larvae hatch and begin to feed on the host’s flesh within 10 to 12 hours. The odor, serum, and blood emitted by infested wounds can attract additional female flies to lay eggs on the host. The NWS lifecycle lasts 18 to 24 days in temperate climates and as long as 2 to 3 months in cool climates.

NWS was eradicated from the United States in 1966 using the Sterile Insect Technique. This technique involves producing sterile flies under lab conditions by exposing 5-to-6-day old fly pupae to gamma radiation. Sterile male flies are then released in areas with known NWS infestation to breed with female flies. These matings result in female flies laying unfertilized eggs and a reduction, and eventual eradication, of the NWS population. Sterile NWS flies are currently produced at a facility in Panama. The USDA has announced plans build an additional sterile insect production facility at Moore Air Force Base in Edinburg, Texas to combat the spread of NWS in Central America and Mexico.

The USDA Response Plan

The USDA’s NWS response goals will be to:

1) Detect, control, and contain NWS as quickly as possible.

2) Eradicate NWS using strategies that seek to stabilize animal agriculture, the food supply, and the economy while protecting public health and the environment.

3) Provide science- and risk-based approaches and systems that facilitate continuity of business for U.S. agriculture.

 

 

 

 

 

 

 

Figure 1: In the event of NWS detection, animal health authorities will use Infested Zones, Adjacent Surveillance Zones, and Fly Surveillance Areas to contain and monitor the spread of NWS.

 Key activities that makeup the NWS response will be to:

1) Coordinate response and communications with stakeholders and the public.

2) Reduce spread to non-infested animals and prevent NWS from establishing in new areas.

3) Manage NWS on infested premises.

4) Implement NWS surveillance and management strategies in wildlife.

5) Implement NWS fly surveillance and management strategies (including sterile insect releases).

6) Maintain continuity of business.

7) Ensure information flow and management.

8) Identify and maintain resource requirements.

Immediate Actions in Event NWS is Suspected or Detected

If NWS is suspected on your property:

• Immediately report the case to your local veterinarian, State Animal Health Official (SAHO), or USDA Area Veterinarian. NWS sample identification will be performed at USDA APHIS approved laboratories.

• Do not move animals off the premise until inspected and cleared by animal health authorities.

• Ensure all wounds are promptly treated to kill larvae and prevent reinfestation.

• Animal health officials will establish Infested Zones a minimum of 20 km (12.4 mi) around areas with suspected and confirmed NWS cases. The size of Infested Zones is based on the daily distance flies can travel (1 to 2 km) and how long flies can travel in their lifetime (10 to 14 days; Figure 1).

• Federal and state authorities will enforce quarantines and movement restrictions on premises located within Infested Zones.

Surveillance and Coordination

Active and passive surveillance are the backbone of early detection:

• USDA and state authorities will trace recent movements of animals, visitors, and potentially infested materials in and out of infested zones to determine the potential for additional NWS cases. Companion animals and wildlife will also be surveilled.

• Infested Zones will be surrounded by 20 km Adjacent Surveillance Zones (Figure 1) that will be used to monitor animals for NWS infestation and presence of NWS using fly traps.

• Fly Surveillance Zones of up to 200 km (124.3 mi; Figure 1) from the center of Infested Zones will also be established as the outer limits of fly surveillance around an Infested Zone.

• Ranchers and veterinary practitioners may also be asked to assist in sample collection, animal inspection and surveillance.

Prevention, Treatment and On-Ranch Biosecurity

Ranchers play a key role in preventing establishment of NWS:

• Regularly inspect cattle for wounds, particularly during calving, branding, dehorning or castration.

• Use approved wound sprays, antiparasitic drugs, and topical insecticides. The FDA is in the process of approving additional animal drugs for the treatment of NWS.

• Properly dispose of carcasses to prevent larvae development. Minimal movement of carcasses is desired to avoid moving larvae to uninfected premises.

• Maintain records of animal movements and new introductions to the herd.

• Maintain records of animals treated for NWS infestation so that proper drug withdrawal periods are followed before animals enter the food chain.

• NWS is not a food safety concern. Meat and animal products processed in accordance with FSIS and state regulations remain safe and marketable.

Livestock Movement and Continuity of Business

To maintain trade and livestock movement during an outbreak:

• Domestic animal premises not located within an Infested Zone and not linked to a suspect premise may move animals in normal channels for intrastate and interstate commerce. There are no movement requirements for animals into an Infested Zone.

• Animals being removed from Infested Zones will require pre-movement physical inspection, documentation of any treatment for NWS, and NWS animal health certificates before movement.

• Both intrastate and interstate animal movement will require animal health certificates. Animal movement will be subject to movement control checkpoints and regulatory inspections at slaughter establishments.

Role of Ranchers in NWS Containment

Vigilance and cooperation are critical to halting the pest’s life cycle:

• Report suspected cases promptly.

• Follow animal health authority guidance on inspections, treatments and movement restrictions.

• Collaborate with local authorities to implement surveillance and wound management.

• Participate in public awareness campaigns and neighbor communications to strengthen community readiness.

Federal and State Support for Ranchers

The USDA leads coordination, with support from state and tribal partners. Cattle ranchers can expect:

• Technical support from APHIS veterinarians and entomologists.

• Access to the National Veterinary Stockpile for testing and treatment supplies.

• Guidance on quarantine zones and compensation eligibility for affected livestock if depopulation is required. General depopulation is not expected for control and eradication of NWS at this time.

Key Takeaways for Ranchers

• Early detection and wound management save herds.

• Cooperate with authorities during surveillance and quarantine efforts.

• Maintain good biosecurity practices year-round.

• NWS does not affect safety of meat products but can devastate herd health and productivity.

• The goal is rapid containment and eradication to protect ranchers, wildlife and trade.

Federal and state animal health authorities have outlined the plan of attack for combating this new, yet old, threat to the livestock industry. However, ranchers have huge role to play in combating NWS by inspecting herd, reporting suspected cases, adhering to movement restrictions, and maintaining the integrity of containment efforts. In the event NWS is detected in the United States, it will take coordination and cooperation among all sectors of the agricultural community to defeat NWS for the second time.

Sources

Disease Response Strategy: New World Screwworm Myiasis. 2018. Foreign Animal Disease Preparedness and Response Plan. United States Department of Agriculture. Riverdale, MD. Accessed 10/21/25.

https://www.aphis.usda.gov/sites/default/files/nws_myiasis_disease_strategy.pdf

New World Screwworm Response Playbook. 2025. United States Department of Agriculture Animal and Plant Health Inspection Service. Riverdale, MD. Accessed 10/21/25.

https://www.aphis.usda.gov/sites/default/files/nws-response-playbook.pdf

New World Screwworm: What the Meat Industry Needs to Know. 2025. The Meat Institute. Arlington, VA. Accessed 10/28/25.

https://www.meatinstitute.org/sites/default/files/documents/New%20World%20Screwworm%20What%20the%20Meat%20Industry%20Needs%20to%20Know.pdf

For More Information

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Dr. Bain Wilson

Rancher Education & Outreach Manager

bain.wilson@ranch-bot.com

+1 (682) 382-9617